Halogen or halogen compound gases are used for various purposes as an etchant gas, a cleaning gas, a raw material, etc. in etching and CVD processes in the manufacture of semiconductors and liquid crystals. Such a highly reactive halogen or halogen compound gas is fed from a cylinder cabinet to an etching or CVD unit.
When the cylinder in the cylinder cabinet is replaced, the reactive halogen or halogen compound gas remaining in the pipeline of the cabinet, such as a gas feed pipe, is exhausted as vent gas before the replacement. The vent gas containing the halogen or halogen compound gas is not allowed to be released into the air so that a unit for removing harmful substances from vent gas must be installed.
Wet methods and dry methods are known as methods using a treating agent for removing highly reactive halogen or halogen compound from exhaust gas.
A wet method is a treatment of the exhaust gas with water or an aqueous solution of sodium hydroxide. Treatment (scrubbing) with water is mostly practiced because treatment with an aqueous solution of sodium hydroxide induces different problems such as wafer contamination. In the case of treatment with water, toxic oxidizing gas and acidic gas could be made non-toxic at high efficiency by using a large quantity of fresh water.
Actually, however, treating (scrubbing) water is used in circulation for the time being in view of the amount of waste water. Therefore, toxic gas has been released without being thoroughly removed from vent gas.
A dry method, on the other hand, is a treatment of exhaust gas with a solid treating agent. Various treating agents have been proposed. For example, Japanese Patent 2778031 proposes an adsorbent for nitrogen oxides and sulfur oxides which comprises calcium sulfate, calcium hydroxide, activated carbon, amorphous carbon, and an alkali metal compound. JP-A-2001-338910 discloses a method of treating halogen-containing gas which comprises the steps of bringing the gas into contact with a treating agent containing iron oxide, an alkaline earth metal compound, and activated carbon and bringing the thus treated gas into contact with a treating agent comprising zeolite.
The above-described adsorbent and treating agent use a large quantity of activated carbon with a large specific surface area to enhance the effect of contact with a halogen compound gas. It is true that a large amount of a halogen compound gas is adsorbed on activated carbon. However, because of the high reducing power of activated carbon, an rapid reaction can occur between the halogen compound gas adsorbed onto the treating agent and activated carbon, which induce an explosion.